Definition of "unsay"

unsay

verb
third-person singular simple present unsays, present participle unsaying, simple past and past participle unsaid
1. To withdraw, retract (something said).
  Quotations
  And in the first place, you will be so good as to unsay that story about selling his head, which if true I take to be good evidence that this harpooneer is stark mad […]
  1851 November 14, Herman Melville, Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley
2. To cause something not to have been said; to make it so that one never said something (since this is physically impossible, usually in the subjunctive).
  Quotations
  Certainly if Chriſts Apoſtle have ſet down but two, then according to his own words, though he himſelf ſhuld unſay it, and not only the Angel of Smyrna, but an Angel from Heaven ſhould bear us down that there be three, Saint Paul has doom'd him twiſe, Let him be accurſt [...]
  1641 June or July, John Milton, Of Prelatical Episcopacy, and Whether It may be Deduc’d from the Apostolical Times by Virtue of Those Testimonies which are Alledg’d to that Purpose in Some Late Treatises; […]; republished in A Complete Collection of the Historical, Political, and Miscellaneous Works of John Milton, […], volume I, Amsterdam [actually London: s.n.], 1698, page 247